1. Field of the Invention
An aspect of the invention relates to a brake apparatus which includes multiple wheel cylinders that apply braking forces to respective multiple cylinders when being supplied with hydraulic fluid; multiple maintaining valves that are arranged upstream of the respective wheel cylinders in order to maintain hydraulic pressures in the respective wheel cylinders; pressure-regulating control valves that are arranged upstream of the multiple maintaining valves in order to control an upstream pressure which is a pressure upstream of the multiple maintaining valves; and a control unit that controls the upstream pressure by switching a pressure-control mode between a pressure-regulating mode which is selected when a deviation of the upstream pressure from a target pressure is outside a setting range and in which the upstream pressure is brought to the target pressure using the pressure-regulating control valve and a pressure-maintaining mode that is selected when the deviation is within the setting range.
2. Description of the Related Art
For example, Japanese Patent Application Publication No. 2006-123889 (JP-A-2006-123889) describes a brake control apparatus that is equipped with so-called brake-by-wire technology. According to the brake-by-wire technology, a brake operation performed by a driver is detected, and a braking force that is required by the driver is generated under electronic control. In the brake control apparatus, paired linear control valves, which are shared by all wheel cylinders, control wheel cylinder pressures in the respective wheel cylinders. In terms of cost performance, providing only one pair of linear control valves is better than providing linear control valves for respective wheel cylinders.
Japanese Patent Application Publication No. 2007-137281 (JP-A-2007-137281) describes a brake control apparatus that executes control by changing a control gain for a linear control valve based on the number of ABS maintaining valves that are open so that fluctuation of the upstream pressure due to opening and closing of the ABS linear maintaining valves is suppressed during ABS control.
When brake assist control is executed to enhance the degree of brake application during a sudden braking operation, ABS control may be executed along with the brake assist control. The reason why the ABS control is executed is that wheel lockup easily occurs because the wheel cylinder pressure is controlled to a relatively high pressure under the brake assist control. The ABS maintaining valves are repeatedly opened and closed under the ABS control, and a volumetric capacity, which is a target of control by the linear control valves, dynamically fluctuates relatively widely. That is, control characteristic of the wheel cylinder upstream pressure, which is the control target hydraulic pressure, fluctuates dynamically. In this case, it is more difficult to bring the wheel cylinder upstream pressure to a target hydraulic pressure than in the case of regular braking control.